Which statement is true about ASM and/ or SSM multicast?

Which statement is true about ASM and/ or SSM multicast?

A.
SSM does not require MSDP.

B.
ASM requires an external mechanism to find the source.

C.
SSM only builds RPT trees, since the RP is replaced by an external mechanism.

D.
ASM and SSM for IPv6 multicast use embedded RP.